The present invention relates to turbine blades. More particularly, the present invention relates to a turbine blade having a cooled tip shroud.
A turbine assembly, such as those used in aircraft, and power generation, typically generates rotating shaft power by expanding hot compressed gas produced by combustion of a fuel. Power generation takes place in the turbine section of the turbine assembly. The turbine assembly employs a number of rotating blades that are affixed to the rotating shaft and include an airfoil portion.
The efficiency of the turbine assembly is limited in part by xe2x80x9cspillover:xe2x80x9d the escape of hot combustion gases through the clearance gap between the turbine blade and the wall of the turbine assembly, which is commonly referred to as the turbine shroud. To reduce spillover, it is a common practice in the art to provide a tip shroud on the end of the airfoil opposite the end attached to the rotating shaft. The tip shroud includes a shelf and, optionally, a blade tooth that reduces spillover by decreasing the size of the clearance gap and interrupting the hot gas path around the end of the turbine blade.
Tip shrouds are subject to creep damage due to the combination of high temperature and centrifugally induced bending stresses. The creep is usually manifested by the formation of xe2x80x9cdog earsxe2x80x9d along unsupported edges of the shelf formed by the tip shroud. xe2x80x9cDog earsxe2x80x9d as used herein, means the folding or degrading of the metal edges of the shelf formed by the tip shroud. Because it has been generally found that reinforcing the shelf simply transfers the stress from tip shroud to the root of the airfoil, the approach to reducing creep in this region of the turbine blade has been to xe2x80x9cscallopxe2x80x9d i.e., remove unsupported portions of the shelf. Scalloping, however, leads to increased hot gas path leakage past the turbine blade. If the tip shroud and shelf could be adequately cooled, the need to scallop the shelf could be substantially reduced. Consequently spillover would also be reduced and turbine efficiency could be improved.
The turbine blade designs that are currently available do not provide adequate cooling to allow the use of a tip shroud having a sufficiently large unsupported shelf that would decrease spillover. Therefore what is needed is a turbine blade that provides sufficient cooling to the tip shroud and shelf. What is also needed is a cooled tip shroud having a shelf that is sufficiently large to prevent spillover.
A turbine blade having a cooled shroud comprises a blade attachment portion and a radially extended turbine airfoil integral with the blade attachment portion. The turbine airfoil has a plurality of cooling passages. A tip shroud is affixed to a top portion of the airfoil, the tip shroud having a plurality of circumferential cooling channels disposed substantially parallel to the rotation of the airfoil. Each circumferential cooling channel is in communication with a respective cooling passage and at least one exit port is in communication with at least one of the circumferential cooling channels.